A particular application that needs positive and negative supply voltages with respect to a common ground potential is an active matrix OLED (organic light-emitting diode) display. Typical supply requirements for such an application are ELVdd=4.0 to 6.0V and ELVss=−5.0 to −8.0V at a current consumption of 15 to 50 mA, depending on brightness and size of the display. For portable solutions, the available supply input voltage usually comes from a lithium-ion (Li-Ion) single cell at a voltage of 2.5 to 5.0V. The target efficiency of the system should be on the order of 80%.
The brightness of the individually-controlled OLED pixels depends heavily on the values of the supply voltages applied to the display panel. Any fluctuation in the supply voltages is recognized as a pattern over the OLED display panel. The tolerated maximum fluctuation in the supply voltage for transients of 0.5V at the converter input is 2 to 5 mV. Standard dual inductor switched mode converters cannot produce such low fluctuation values (i.e., high power rejection ratio). To achieve the required low level of fluctuations, additional linear voltage regulators are needed. The additional linear voltage regulators, however, reduce the overall power efficiency of the system.